Julia Gillard and Tony Abbott are at loggerheads over a 1 per cent reduction in company taxes paid for by the Government's contentious minerals resource rent tax (MRRT).

The MRRT is within days of becoming law, but the row over the company tax cuts has placed the entire measure in jeopardy.

The Greens and the Coalition are both refusing to allow the tax cut to go through the Senate.

Mr Abbott, who toured a solar energy business in Canberra, says he does not support the cut because it is dependent on higher taxes for the mining sector.

"What we've said very consistently ever since the Government first announced the mining tax is that we don't support the new tax, and we don't support the measures associated with the new tax," he said.

"A tax cut that's paid for with a tax increase is not a cut, it's a con. It's a tax fiddle, not a tax reduction."

Mr Abbott has instead restated the Coalition's promise of a "modest" company tax cut, but he would not say when it would be introduced or how much it would be.

"It is the Coalition's firm commitment, our strong policy, to deliver a modest company tax cut at the next election and all our policies will be fully funded," he said.

"What you'll get under us are tax cuts without new taxes.

"What you're getting under Labor are tax cuts that are funded by new taxes, and a tax cut that's paid for with a tax increase."

Tax break

The Greens want the 1 per cent company tax cut restricted to small business.

Greens leader Bob Brown says it "doesn't make sense" to give big business a tax break.

"The Government may have made a commitment to this, but times have changed and it's time the Government changed this commitment and dropped this proposal," he said.

The Greens hold the balance of power in the Senate and, with Coalition votes, could well succeed in blocking the Government's plan.

They have agreed to pass the initial mining tax legislation though, which the Government believes will pass the Senate on Monday.

Senator Brown has suggested that the definition of a small business be extended, from a $2 million per annum turnover to $5 million, to ensure more companies benefit.

"The Greens will be able to, on current indications, prevent the tax cut from going to the wealthy corporate sector but ensure that it still goes to small business in this country," he said.

Ms Gillard has refused to say whether she is willing to compromise with the Greens.

"The Government's position today is crystal clear," she told reporters at a Canberra book shop.

"We're for taking a fair share of tax from the turbo-charged section of the economy - the resources sector - and using that to benefit businesses around the nation big and small."

Surprised

But Ms Gillard was unequivocal in her criticism of the Opposition's stance.

"I am very worried about the uncertainty that Tony Abbott's created today," she said.

"This is proof that Mr Abbott has become so negative that he is planning to vote against tax cuts for small business, vote against jobs, and vote against the Australian economy."

She says she has been "truly surprised" by Mr Abbott's opposition to a business tax cut.

"I never thought I would see the day that the Liberal Party would join with the Greens to vote against a tax cut for business," he said.

The business sector is crying out for the cut which would reduce company taxes from 30 per cent to 29 per cent this year for small businesses.

Australian Industry Group chief executive Heather Ridout has urged the Greens to reconsider.

"The origin of the tax cut for Australian companies was the Henry Tax Review report, which recommended that the company tax rate be cut to 25 per cent as part of efforts to address the impact on Australian companies on the wrong side of the mining boom," she said.

"Twenty-nine per cent is the bare minimum required and but a start. And as envisaged by Henry the cut should be available to companies of all sizes."